Epoxy resins are known to have excellent heat-resistant, adhesive, antichemical, electrical, mechanical and other properties and, therefore, have extensively been used in various fields as adhesives, coatings, sealants, insulating materials, casting and molding materials and the like.
Two systems are employed to harden or cure the epoxy resin; one using a polyamine or polycarboxylic acid or anhydride hardener and the other being a self-polymerization system containing a cationic or anionic polymerization initiator generally referred to as "curing catalyst".
A variety of curing catalyst are known including Bronsted acids, Lewis acid, tertiary amine-superacid salts and the like. These known curing catalysts have certain defects in that they are solid or not soluble in conventional solvents such as toluene or are xylene or not fully compatible with the epoxy resin so that they can be uniformly dispersed in the epoxy resin only with difficulty. This can result in incomplete or localized curing of the resin. Furthermore, the prior art curing catalysts are generally capable of curing of alicyclic epoxy compounds or resins at room temperature but not non-alicyclic epoxy compounds or resins which are less reactive than the alicyclic epoxy resins.
A need exists, therefore, for a curing catalyst of epoxy resins which is soluble in conventional organic solvents such as toluene and xylene, highly compatible with epoxy resins and capable of curing non-alicyclic epoxy compounds or resins at room temperature. Also, a need exists for a resinous composition containing a polyfuctional epoxy compound or resin and such a hardening catalyst.